It is desired to control access to many existing cellular radio communication systems in order to more efficiently use radio resources available. By controlling the access, load on the communication systems may be controlled, i.e. a reduced number of users implies a reduced load. Since radio resource often is a limited resource, it may be desired to allow some users of the cellular radio communication system access at the expense of not allowing some other users access to the cellular system.
For a Long Term Evolution (LTE) system, one such known method is called Access Class Barring (ACB). The LTE system may comprise a user equipment (UE) and a radio base station, often referred to as eNodeB (abbreviated eNB). The UE is a member of an Access Class (AC), which is stored in the universal subscriber information module (USIM). It shall be noted that the UE may be a member of one or more Access Classes. The eNB may announce an ACB state in a cell, managed by the eNB, through system information (SI). The system information may be broadcast by the eNB. A System Information Block Type 2 (SIB 2) of the system information lists the state of each AC through an Access Class Barring Factor (ACBF) associated with each AC. The ACBF has a value between 0 and 1. When the UE receives an SI and finds an AC in the SI, the UE checks if the AC, found in the SI, corresponds to the AC stored in the USIM. If the ACs match, the UE generates a random value between 0 and 1. If the random value is lower than the ACBF of the AC, the UE considers the cell as barred. That is, the UE is not allowed to send an access request to the cell for a random time period with a mean value governed by the Access Class Barring Time (ACBT) parameter included in the SI, more specifically in SIB 2.
The SIB 2 of the SI is transmitted with a periodicity of 80 ms or more. This may cause the access restrictions to be too slowly updated. Furthermore, updates of the SI is restricted by certain rules, which limit the frequency with which updates may occur and how fast an update may occur after being triggered. These rules include the concept of modification period, whose length is configurable in the SI and may be as long as 41 seconds. In addition, with certain exceptions, such as Earthquake and Tsunami Warning System (ETWS) information, and Commercial Mobile Alert System (CMAS) information and certain regularly changing parameters, it is not allowed to update the SI more than 31 times in a 3 hour period.
In WO 2010/057540, there is disclosed a method for providing a contention based data transmission from user equipments. In general, contention based data transmission refers to a transmission mode where a wireless entity, e.g. a user equipment, transmits data without having a dedicated radio resource allocated for this transmission. Instead, a radio resource is used, which may also be used by other wireless entities. If two or more wireless entities simultaneously attempt to transmit data using the same radio resource, a collision occurs (i.e. the transmissions interfere with each other), which typically means that the receiver(s) of the transmissions cannot correctly receive all the transmissions and, in the worst case, fail(s) to correctly receive even one of them. Hence, in order to allow the receiver to correctly receive the data of an incorrectly received transmission, the sender has to retransmit the data. In line with this general description of contention based data transmission, WO 2010/057540 discloses how user equipments are adapted to transmit data using resource blocks allocated by a radio network for contention based data transmission. The radio network is adapted to allocate resource blocks to a dedicated one of the user equipments or to a plurality of user equipments, with the latter being used for contention based data transmission. The radio network node allocates at least one resource block, which will be referred to as a contention based resource in the paragraph following the next paragraph, that is not allocated to any dedicated user equipment, but to a first plurality of the user equipments. The allocation is signalled to the user equipments. A first user equipment of said plurality of user equipments obtains data for transmission and transmits it using said at least one resource block. When two or more user equipments of said plurality of user equipments attempt to transmit data at the same time a collision occurs, i.e. more than one user equipment attempt to access the contention based resource at the same time. A collision frequency may be measured to keep track of how often collisions occur. In this manner, contention based data transmission in the uplink is enabled without prior scheduling request and scheduling grant. As a result, delays in uplink transmission resulting from scheduling request and scheduling grant are reduced.
Such contention based data transmission may be useful in conjunction with machine-to-machine communication involving large numbers of Machine Type Communication (MTC) devices, because a MTC device may infrequently access the radio network to send small pieces of data, such as measurement data in case the MTC device is equipped with a temperature sensor or the like. The MTC device will therefore in such scenarios have an undesirably high signalling-to-user data volume ratio. This means that control signalling overhead is undesirably large. Moreover, the MTC device is typically power constrained, i.e. the MTC device may be powered by a battery which eventually will be drained from power. Thus, there is a need for reduced control signalling overhead and this may be achieved through the contention based data transmission described above.
Moreover, if load on the contention based resources increases, the collision frequency will also increase and will eventually become so high that its negative impact on system properties, such as throughput, access delay and resource efficiency, as well as increased overhead on the UEs' data transmissions due to retransmissions, outweighs the benefits of the contention based (CB) mode. As a countermeasure, the eNB may limit the number of access attempts using the CB resources. The ACB mechanism described above cannot be used for this purpose, because it restricts access to the entire cell, i.e. to all access resources in the cell rather than only the contention based resources. Therefore, it has been proposed to allow the eNB to associate an access probability with a CB resource. The access probability is announced in the SI or signalled to the UEs via radio resource control (RRC) signalling. For MTC devices it may not be a completely satisfying solution, since large and rather rapid load variations on the CB resources may often occur for MTC devices. A reason for this may be that many MTC devices may more or less synchronously be triggered to send an uplink (UL) data transmission. Such synchronization may result from, for example, when multiple sensors of respective MTC devices detect that alarms need to be transmitted as uplink transmissions, or when multiple sensors detect that a failure, or a sequence of related failures, has/have occurred and hence need to transmit notifications of the failure as uplink transmissions. As another example, groups of MTC devices running the same application with synchronized periodic reporting periods may also generate such synchronization of uplink data transmission.
Therefore, there is a need for an alternative or additional method of providing access restriction information to a user equipment, such as an MTC device, which allows the MTC device to consume less power and which may update the access restriction information more frequently than with present methods, such as Access Class Barring.